Novak Djokovic, beaten twice in the past month and nursing an ankle injury, is sounding a little uncertain about his clay-court campaign. The world No1, who fell heavily during Serbia's Davis Cup win over the United States last week, says he will wait until Tuesday before deciding if he is fit to play in this week's Monte Carlo Masters.

"I can't guarantee 100% that I'll be on court," he said on Sunday. "I have to be realistic and cautious."

The only reason he contemplated playing was because he has a second home in the tax haven – and, if he is not able to fulfil a Masters 1000 obligation in his adopted city, he must be concerned about his upcoming timetable, leading into the French Open in late May.

"I've had three days of practice and I've been increasing the level each day," he said. "If I have discomfort over the next two days that would be an indication if I should or should not play. This is the start of a new season on a new surface. To compete at a high level I must be 100% fit. I've been taping the ankle and doing all I can to be ready on the court. I know there is a lot of expectation for me to play – no one wants me to be out there more than I do."

Djokovic is on the other side of the draw from Andy Murray, who is within a couple of tournament wins of supplanting his long-time rival at the top of the rankings. They practised together on Saturday.

"I practised well in Miami," Murray said, refreshed after a draining triumph in the final there over David Ferrer that elevated him to No2 behind Djokovic and ahead of Roger Federer, who is taking a two-month break. "I feel good."

He will not feel so rosy if he doesn't reach the quarter-finals, however, as Federer would leap-frog him in the rankings again. Murray has a first-round bye, then plays either a qualifier or the Dutchman Robin Haase, followed, probably, by Stanislas Wawrinka with every prospect of meeting Rafael Nadal in the semis.

"It's a tough draw," Murray said. "It always is here. At the Masters 1000s, where you have the smaller draws, there are not many easy matches."

Nadal, reaching for his ninth title in Monte Carlo, is rebuilding his aura menacingly, and two contenders made respectful noises on Sunday about the winner of 17 out of 18 matches since his comeback from a seven-month lay-off to rest his troubled knees. The Frenchman Richard Gasquet called him "a bull", while his compatriot Jeremy Chardy described him as a "lion".

Whatever sort of animal he is, Nadal is a warm favourite to reach the final, and whoever is across the net from him this week will know they've been in a fight.

Another of the many tennis players with a home in Monte Carlo, the temperamental Australian Bernard Tomic, lost in straight sets to Alexander Dolgopolov in the opening round. The Ukrainian beat him here in the second round last year. Also through are former quarter-finalist Philipp Kohlschreiber and the Bulgarian prospect Grigor Dimitrov.